It is currently possible to transmit audiovisual programs in digital form via broadcasting networks of the microwave (herzian), cable, satellite type, etc. or via telecommunication networks of the DSL type (Digital Subscriber Line) or BLA type of (Local Radio Loop) or via DAB networks (Digital Audio Broadcasting) as well as via any wireless telecommunication network of the GSM, GPRS, EDGE, UMTS, Bluetooth, WiFi types, etc. Moreover, works broadcast in this manner are frequently encrypted or scrambled by various means to avoid pirating.
As concerns the distributed systems based on the client-server principle characterized by “caching,” there are also two main types of systems that are classified according to the content treated by this “caching” characterizing an intermediate server also called “cache” server. The term “caching” denotes the possibility of being able to temporarily hold a copy of contents or of data (permanently stored in a central server) at a point or at different points of the network (e.g., intermediate servers) to serve the requests of clients the closest to these points and thus reduce the overload on the central data server and consequently optimize the transmission rate used on the intermediate servers.
The first type processes data whose distribution has no time restrictions (systems for the distribution of files by “caching”) and the second type concerns the processing of multimedia (audio/video) data.
The systems for conventional distributed files such as Sun NFS, Apollo Domain, Andrew, IBM AIX, DS, AT&T RFS perform the “caching” of files locally, do not have the possibility of making the “caching” of files in proximate or remote nodes and can not allocate local servers for applying the “caching” to files. Moreover, the conventional distributed systems characterized by “caching” have a granularity of the size of a file and, consequently, the possibilities of having a scalability of the distribution of the contents via the network are greatly reduced.
On the other hand, other distributed multimedia systems characterized by “caching” such as the “Berkeley Distributed VOD,” for example, do not obtain a “caching” that is completely secure and personalized for each user, have limited capacities of scalability and are frequently penalized by the limited bandwidth of the networks.
GRIWODZ C and AL “Protecting VOD the Easier Way,” XP000977484-ACM 1998 dated Sep. 12, 1998 discloses a method for protecting an MPEG-1 video stream to make it publicly available by cache servers. Protection of the video stream is carried out by a separation of complementary information. The protected video stream contains a corrupted part that is inserted in advance at the site of the separated information.
The corrupted data is independent of the data of the main stream. It is selected by using a calculating algorithm that minimizes attacks by correlation with the protected video stream. The protected video stream is not necessarily in conformity with the MPEG-1 format, that is the format of the main video stream. Then, the method uses “point-to-point” connections (unicast) to supply the complementary part of the data.
The complementary information comprises billing information, user identification information and information for tracing pirates of reproduction rights (by placing watermark mechanisms). The replacement corrects the corrupted part of the data. The complementary information is transmitted to the client by point-to-point (unicast). That part is encrypted at the server by a personal key that can be produced by a trusted third party.
That disclosure responds in particular to the question of scalability for the main video stream by securing the stream with the corruption method; however, that disclosure does not respond to the question of scalability nor to security nor to the distribution of complementary information in the case of networks with a limited bandwidth and a high delay and jitter value such as, e.g., networks of the GSM or GPRS types.
FR 2835386 relates to a video and multimedia interface arrangement of the MPEG-4 type to connect at least one display device to at least one video source, constituted substantially on the one hand of a processing unit adapted in such a manner as to display any video stream of the MPEG-4 type in real or deferred time, store it, record it and/or send it to a broadcasting network and/or to a low bandwidth extended telecommunication network and/or record it on a smart card, and on the other hand by at least one screen interface and one interface for connection to a local or extended network and/or to a smart-card reader, characterized in that it comprises substantially on the one hand a memory of certain correlation coefficients of the I-VOP and/or P-VOP planes and/or a memory of certain B-VOP and P-VOP planes of the video stream in each audiovisual portal, and that on the other hand that each video interface arrangement has functions of storage, recording and processing of audiovisual programs and is associated with at least one apparatus of the integrated display type or of the television screen type, and that each video interface arrangement reconstitutes the MPEG-4 streams coming from information on its own hard disk and algorithms and/or correlation coefficients of the I-VOP and/or P-VOP planes, and/or P-VOP and/or B-VOP planes, all of which comes from the portal.
The technical means consist of proceeding, prior to transmission to the client's equipment, to an analysis of the stream to generate a first modified stream having the format of a nominal stream, and a second stream with any format comprising the digital information suitable for permitting the reconstruction of the modified planes, then in separately transmitting the two streams generated in this manner from the server to the addressee's equipment, and in that a synthesis of a stream in the nominal format is calculated on the addressee's equipment as a function of the first stream and of the second stream.
That disclosure addresses in particular the issue of protection of the video stream of the MPET-4 type by separation of complementary information and the secure sending of the complementary information to the client portal using a secure element such as a smart card. That disclosure does not respond to the question of scalability for the distribution of the complementary information. It also does not respond to the question of securing the information at the cache points or intermediary servers on the network. This latter is characterized by a limited bandwidth and a high delay and jitter value such as, e.g., a network of the GSM or GPRS type.